The present invention relates to a permanent-magnet electric motor for circulation pumps of heating systems.
The circulation pumps of heating systems are currently substantially constituted by a centrifugal pump coupled to an asynchronous. electric motor.
The stator is substantially composed of a toroidal lamination pack to which electric windings are coupled.
The rotor is constituted by a shaft and by a lamination pack to which the shaft is coupled.
The lamination pack accommodates a squirrel-cage circuit.
The rotor is immersed in a fluid to be forced into the system and therefore, in order to avoid corrosion of the metallic parts, particularly of the lamination pack (since the conductors of the squirrel-cage circuit are made of copper), the rotor is protected by means of a stainless steel jacket.
The rotor is arranged in a cylindrical chamber which is separated with a watertight seal from the stator and is usually formed by a metallic tubular element.
It is known that for good operation of asynchronous motors, the gap between the rotor and the stator must be reduced to a minimum.
In known motors, the gap has minimum limits which are constituted in practice by the thickness of the metallic tubular element forming the rotation chamber of the rotor, by the stainless steel jacket protecting the rotor, and by the space required (mainly dependent on machining tolerance) between the rotor and the tubular element.
The fundamental need to minimize the gap in circulation pumps of heating systems, however, clashes with the need to adequately dissipate the heat produced by the stator windings, bearing also in mind that the temperature of the circulation water can be as high as 95xc2x0 C.
The rotor is immersed in water due to the connection of its chamber to the chamber of the impeller, but the fluid film that forms between the rotor and the walls of the chamber is too small to allow an adequate heat exchange between the stator and the water.
Furthermore, the fact that the space between the rotor and the chamber is inevitably limited entails the real possibility of rotor jamming, mainly due to dirt which can infiltrate into the empty spaces.
Another consequence is insufficient evacuation of the air bubbles that form especially during the installation and filling of the hydraulic circuit and subsequently when the pressure increases due to the temperature.
The presence of air inside the pump is annoying because it generates noise and most of all may seriously compromise the duration of the bushes that support the rotor shaft.
For this reason, known motors have a vent screw placed in the rear part of the rotor chamber.
The screw is also meant to release the rotor when dirt prevents it from rotating.
Furthermore, the fact that the element for separating the fluid circulating in the rotor chamber and the active parts of the stator (iron, copper) is made of a material which is not electrically insulating forces the manufacturer to ground the electric circuit, with obvious constructive complications which affect costs.
The aim of the present invention is to provide an electric motor for circulation pumps of heating systems having such a structure which allows to eliminate or substantially reduce the problems noted above in conventional motors.
Within the scope of the above aim, a consequent primary object of the invention is to provide a motor which is compact and constructively solid.
Another important object is to provide an electric motor having a structure which is capable of providing good heat dissipation into the environment.
Another object of the invention is to provide a motor whose structure can integrate a plurality of components and therefore achieves considerable benefits in terms of simplicity of assembly.
Another object of the invention is to provide a motor having a structure which is competitive with respect to conventional motors also from the point of view of costs.
This aim and these and other objects which will become better apparent hereinafter are achieved by a permanent-magnet electric motor for circulation pumps of heating systems, comprising:
a stator composed of a pack of metallic laminations which form pole shoes to which electrical windings are coupled;
a permanent-magnet rotor, arranged in a chamber separated with a watertight seal and electrically insulated from the stator;
characterized in that said chamber that contains the rotor has a cross-section which duplicates the contour of the pole shoes in regions affected by said pole shoes and is shaped so as to form wider portions in regions that are not affected by said pole shoes.
Advantageously, the cross-section of said chamber that contains the rotor is substantially square, with central regions of the sides which widen in an arc-like shape.